1. Field of the Invention
The present invention relates to a thin film transistor, a display device including the thin film transistor, and a method of manufacturing the display device.
2. Description of the Related Art
Display devices, such as liquid crystal displays, organic light emitting diode (OLED) displays, and electrophoretic displays, include a plurality of pixels. Each of the pixels includes a pair of electromagnetic field generating electrodes and an optical active layer therebetween. For example, a liquid crystal displays includes a liquid crystal capacitor where a liquid crystal layer is interposed between electromagnetic field generating electrodes as an optical active layer, and an OLED display includes an OLED element where an organic light emitting layer is interposed between electromagnetic field generating electrodes as an optical active layer.
The display device includes a switching element connected to one of a pair of field-forming electrodes to switch an electrical signal, and an optical active layer converts the electrical signal into an optical signal, thereby displaying an image. Here, the switching element receives a data signal from a data line according to a scanning signal from a gate line to transmit the data signal to a pixel electrode, and typically consists of thin film transistors.
The field-forming electrodes, the switching element, the gate line, the data line, and the like are provided on one or more display panels.
The display device includes a gate driver that applies scanning signals to gate lines and a data driver that applies data signals to data lines. The gate driver and the data driver are driven by control signals transmitted from a signal controller, and the like. In recent years, attempts have been frequently made to form the gate driver and the data driver on the same display panel with the field-forming electrodes, the switching element, and the like. In such cases, the gate driver and the data driver include active elements made of thin film transistors.
Meanwhile, an OLED display may further include a driving transistor as well as a switching element to allow electric current to flow through an organic light emitting diode according to the data signal supplied from the switching element.
Due to high mobility and on-current, a thin film transistor using a polycrystalline semiconductor (or a polycrystalline-semiconductor thin film transistor) draws much attention as an element required for a gate or data driving integrated circuit (IC) mounted on a display panel together with a switching element.
In order to manufacture the polycrystalline-semiconductor thin film transistor, however, a crystallization process, an impurity injection process, and an activation process are additionally required. Moreover, the thin film transistor has many restrictions on its application as a switching element of a pixel unit due to a higher leakage current than a conventional thin film transistor using an amorphous semiconductor (or amorphous-semiconductor thin film transistor).
In this situation, there have been active attempts to form a driving unit with a polycrystalline-semiconductor thin film transistor and form a pixel unit with an amorphous-semiconductor thin film transistor by exploiting unique advantages of the polycrystalline-semiconductor thin film transistor and the amorphous-semiconductor thin film transistor. By forming the polycrystalline-semiconductor thin film transistor simultaneously with formation of the amorphous-semiconductor thin film transistor without a need for a separate mask process, additional cost and time can be minimized.
As mentioned above, in spite of high mobility, the polycrystalline-semiconductor thin film transistor reduces an operation range of a driving IC due to its high leakage current.
Moreover, in a general thin film transistor having an inverted stagger structure, a channel region is defined by a source pattern and a drain pattern. For this reason, the etching dispersion of source and drain patterns is reflected into the electric characteristic dispersion of the thin film transistor.